There is an EGR cooler where numerous, round in section, straight tubes are juxtaposed apart from one another, with both ends of the tubes communicating with headers and outer peripheries of the tubes being covered with a casing. This is a cooler that allows cooling water to circulate within the casing, allows exhaust gases to circulate within the tubes, and conducts heat exchange between both to cool the exhaust gases.
As another EGR cooler, an invention has been proposed in Japanese Patent Application Laid-Open Publication No. 2000-345925, in which plural spiral-shaped protrusions are formed on inner peripheral surfaces of the tubes so that the exhaust gases sufficiently contact the inner peripheral surfaces of the tubes.
Although it can to a certain extent be expected that conventional EGR cooler tubes having plural spiral-shaped protrusions formed on the inner surface sides thereof further improve contact between the exhaust gases and the inner peripheral surfaces of the tubes, it is difficult to say that the improvement is sufficient in and of itself.
Thus, it is an object of the present invention to provide an EGR cooler that can sufficiently agitate exhaust gases within tubes, accelerate heat exchange, and is easy to manufacture. Moreover, sometimes condensate liquid is generated within the tubes, and in this case it is an object of the invention to be able smoothly eliminate such condensate liquid.